Rubber composite

ABSTRACT

PCT No. PCT/JP88/00983 Sec. 371 Date May 25, 1989 Sec. 102(e) Date May 25, 1989 PCT Filed Sep. 28, 1988 PCT Pub. No. WO89/02908 PCT Pub. Date Apr. 6, 1989.A rubber composite comprising polyester fibers as the reinforcing material, wherein a compound having at least one cyclic imino ether group of a specific structure in its molecule is incorporated in a rubber composite except for adhesive-treated polyester cords.

This application is a division of now abandoned U.S. application Ser.No. 07/362,419 filed May 25, 1989.

DESCRIPTION

1. Technical Field

The present invention relates mainly to a rubber composite such astires, belts, hoses, etc. in which polyester high-tenacity fibers forindustrial materials are used, and more particularly to a rubbercomposite to which special additives are added and which is suitable foruses in which said polyester high-tenacity fibers, a reinforcingmaterial for the rubber composite, suffer degradation during use andprocessing, said degradation being caused by the participation of aminesderived from the additives in the rubber.

2. Background Art

Presently used rubber composites with polyester high-tenacity fibers asa reinforcing material, for example tires, have a problem that, whenused at high temperatures resulting from their own heat build-up or thetemperature of the environment, the polyester high-tenacity fibers, areinforcing material, have a lower tensile strength and adhesionstrength. It has long been recognized that this thermochemical stabilityin rubber is a serious problem for the polyester fibers, and W. W.Daniels, et al. proposed, as early as 1959, to improve the chemicalstability by reducing the content of terminal carboxyl groups to 15equivalents/10⁶ g or less (Japanese Patent Publication No. 5821/1962).After that, a large number of concrete methods for reducing the contentof terminal carboxyl groups in the polyester fibers have also beenproposed, as shown for example in U.S. Pat. No. 3975329 and JapanesePatent Kokai No. 116816/1980. Further, there have been disclosedtechniques of improving the thermochemical stability of the polyester inrubber by removing moisture from rubber composites by incorporatingcalcium oxide (Japanese Patent Kokai No. 29471/1972) or isatonicanhydride (Japanese Patent Publication No. 36276/1975) in the rubber, orremoving amides from rubber composites by incorporating2-chloro-4,6-diamino-S-triazine (Negodeg PE™) in the rubber (FrenchPatent No. 2066198). In recent years, quite a novel method was disclosedby the present inventors in which the mobility of amorphous chains ofthe polyester is reduced in order to reduce the permeability of aminesin the rubber composite to the polyester (Japanese Patent Kokai No.224879/1985, 12952/1986 and 146876/1986).

DISCLOSURE OF THE INVENTION

However, according to the inventors' study on the degradation of thepolyester in rubber {Yabuki and Sawada, Sen'i Gakkai-shi, Vol. 41, No.11, T-467 (1985)}, the degradation of the polyester is hydrolysiscatalyzed mainly by amines, and the terminal carboxyl groups hardly actas an acid catalyst for the hydrolysis.

(1) Consequently, the techniques to decrease the content of carboxylgroups disclosed in the literature, including Japanese PatentPublication No. 5821/1962, are not so effective to prevent the polyesterfrom degradation.

(2) The techniques to remove moisture from rubber, which are disclosedin Japanese Patent Kokai No. 29471/1972 and Japanese Patent PublicationNo. 36276/1975, cannot maintain the effect because the moisture ofrubber composites is supplied from the outside.

(3) The technique to remove amines disclosed in French Patent No.2066198 has this effect, although it is a technique which was developedwith such mechanism as described in detail in the present inventionremaining unknown. It is a matter of regret, however, that when saidcompound is incorporated in rubber, scorch breaks out to make itdifficult to put the rubber to practical use.

(4) The present inventors' prior application (Japanese Patent Kokai No.224879/1985) is a technique based on a unique idea, but in principle, ithas no effect to prevent the thermochemical degradation at the adhesioninterface between the polyester surface and rubber, and therefore thereis a limitation to the use of this technique.

An object of the present invention is to eliminate the aboveconventional drawback of rubber composites with polyester high-tenacityfibers as a reinforcing material, i.e. a drawback that the chemicalstability of the reinforcing material is poor when the composites areused at high temperatures, by a technique which can be applied toindustry.

A means for solving the above problem, i.e. the constitution of thepresent invention, is a rubber composite with polyester fibers as areinforcing material containing a compound having at least one cycliciminoether group represented by the formula (I) in the molecule,##STR1## wherein X represents an ethylene group, substituted ethylenegroup, trimethylene group or substituted trimethylene group which makesthe cyclic structure of the formula (I) a five-membered or six-memberedring, in the rubber matrix excluding the portion of the adhesive-treatedpolyester fibers.

As the rubber constituting the rubber composite of the presentinvention, there are mentioned natural rubbers, synthetic rubbers suchas styrene/butadiene rubbers, acrylonitrile/butadiene rubbers, butylrubbers, chloroprene rubbers, ethylene/propylene rubbers, etc. andmixtures thereof.

As the polyester fibers constituting the rubber composite of the presentinvention, there are mentioned copolyesters or homopolyesters containingan ethylene terephthalate unit, a polybutylene terephthalate unit or apolyethylene naphthalate unit; polyarylates (wholly aromatic polyesters)whose material is terephthalic acid, isophthalic acid,2,6-naphthalenedicarboxylic acid, 2,6-acetoxynaphthoic acid,4,4'-acetoxybiphenyl, diacetoxyhydroquinone, cyclohexane dimethanol,p-oxybenzoic acid or their derivatives; etc. However, the polyesterfibers of the present invention are not limited to these, specificexamples, and the present invention is effective for fibers composed oflinear-chain high molecular compounds connected mainly through esterlinkages. The foregoing polyester fibers need to be adhesive-treated inadvance in order to obtain solid adhesion between the fibers and rubber.As the adhesive, a mixture of a resorcinol/formalin initial condensate,generally called RFL, and a latex, and an adhesion promotor such asepoxy resins, Vulcabond E (produced by Vulnax Co.), etc. are used. Inthe present invention, however, any adhesive which can give solidadhesion between the polyester fibers and rubber may be used.

As the additives for the rubber composite of the present invention, acompound is used which contains at least one cyclic iminoether grouprepresented by the formula (I), ##STR2## wherein X represents anethylene group, substituted ethylene group, trimethylene group orsubstituted trimethylene group which makes the cyclic structure of theformula (I) a five-membered or six-membered ring, in the molecule.

The cyclic iminoether structure represented by the formula (I) is anoxazoline ring when it has a five-membered structure, and an oxazinering when it has a six-membered structure. X represents an ethylenegroup, substituted ethylene group, trimethylene group or substitutedtrimethylene group, and among these, those having no substituent arepreferred. As the substituent, there are mentioned C₁ -C₁₀ alkyl groupssuch as methyl, ethyl, propyl, butyl, pentyl, hexamethyl, octamethyl,nonamethyl, decamethyl, dimethylmethyl, etc.; C₆ -C₁₂ aryl groups suchas phenylene, naphthyl, diphenyl, etc.; C₅ -C₁₂ cycloalkyl groups suchas cyclohexyl; other C₈ -C₂₀ aralkyl groups, etc.

Specific examples of the compound containing at least one of the abovering structures in the molecule include the following : Monooxazolinecompounds such as 2-oxazoline, 2-methyl-2-oxazoline,2-ethyl-2-oxazoline, 2-propyl-2-oxazoline, 2-butyl-2-oxazoline,2-pentyl-2-oxazoline, 2-hexyl-2-oxazoline, 2-heptyl-2-oxazoline,2-undecyl-2-oxazoline, 2-heptadecyl-2-oxazoline, 2-phenyl-2-oxazoline,2-cyclohexyl-2-oxazoline, 2-benzyl-2-oxazoline, 2-naphthyl-2-oxazoline,2-dichloromethyl-2-oxazoline, 2-trichloromethyl-2-oxazoline,2-chlorophenyl-2-oxazoline, 2-phenyl-4-methyl-2-oxazoline,2-phenyl-4-ethyl-2-oxazoline, 2-phenyl-4,4-dimethyl-2-oxazoline,2-phenyl-5-methyl-2-oxazoline, etc.; bisoxazoline compounds such as2,2'-bis(2-oxazoline), 2,2'-bis(4-methyl-2-oxazoline),2,2'-bis(4,4-dimethyl-2-oxazoline), 2,2'-bis(4-ethyl-2-oxazoline),2,2'-bis(4,4-diethyl-2-oxazoline), 2,2'-bis(4-propyl-2-oxazoline),2,2'-bis(4-butyl-2-oxazoline), 2,2'-bis(4-hexyl-2-oxazoline),2,2'-bis(4-phenyl-2-oxazoline), 2,2'-bis(4-cyclohexyl-2-oxazoline),2,2'-bis(4-benzyl-2-oxazoline), 2,2'-ethylenebis(2-oxazoline),2,2'-tetramethylenebis(2-oxazoline), 2,2'-hexamethylenebis(2-oxazoline),2,2'-octamethylenebis(2-oxazoline), 2,2'-decamethylenebis(2-oxazoline),2,2'-ethylenebis(4-methyl-2-oxazoline),2,2'-tetramethylenebis(4,4-dimethyl-2-oxazoline),2,2'-(1,3-phenylene)bis(2-oxazoline),2,2'-(1,4-phenylene)bis(2-oxazoline),2,2'-(1,2-phenylene)bis(2-oxazoline), etc.; monooxazine compounds suchas 5,6-dihydro-4H-1,3-oxazine, 2-methyl-5,6-dihydro-4H-1,3-oxazine,2-ethyl-5,6-dihydro- 4H-1,3-oxazine,2-propyl-5,6-dihydro-4H-1,3-oxazine, 2-butyl-5,6-dihydro-H-1,3-oxazine,2-pentyl-5,6-dihydro-4H-1,3-oxazine,2-phenyl-5,6-dihydro-4H-1,3-oxazine,2-perfluoroheptyl-5,6-dihydro-4H-1,3-dihydro-4H-1,3-oxazine), etc.; andbisoxazine compounds such as 2,2'-bis(5,6-dihydro-4H-1,3-oxazine),2,2'-methylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-ethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-propylenebis(5,6-dihydro-4H-1,3-oxazine2,2'-butylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-hexamethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-(1,3-phenylene)bis(5,6-dihydro-4H-1,3-oxazine),2,2'-(1,4-phenylene)bis(5,6-dihydro-4H-1,3-oxazine), etc. More preferredcompounds include monooxazoline compounds such as 2-oxazoline,2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-propyl-2-oxazoline,2-butyl-2-oxazoline, 2-pentyl-2-oxazoline, 2-hexyl-2-oxazoline,2-heptyl-2-oxazoline, 2-undecyl-2-oxazoline, 2-heptadecyl-2-oxazoline,2-phenyl-2-oxazoline, 2-cyclohexyl-2-oxazoline, 2-benzyl-2-oxazoline,2-naphthyl-2-oxazoline, 2-dichloromethyl-2-oxazoline,2-trichloromethyl-2-oxazoline, 2-chlorophenyl-2-oxazoline, etc.;bisoxazoline compounds such as 2,2'-bis(2-oxazoline),2,2'-ethylenebis(2-oxazoline), 2,2'-tetramethylenebis(2-oxazoline),2,2'-hexamethylenebis(2-oxazoline), 2,2'-octamethylenebis(2-oxazoline),2,2'-decamethylenebis(2-oxazoline), 2,2'(1,3-phenylene)bis(2-oxazoline),2,2'-(1,4-phenylene)bis(2-oxazoline), etc.; monooxazine compounds suchas 5,6-dihydro-4H-1,3-oxazine, 2-methyl-5,6-dihydro-4H-1,3-oxazine,2-ethyl-5,6-dihydro-4H-1,3-oxazine, 2-propyl-5,6-dihydro-4H-1,3-oxazine, 2-butyl-5,6-dihydro-4H-1,3-oxazine,2-pentyl-5,6-dihydro-4H-1,3-oxazine,2-phenyl-5,6-dihydro-4H-1,3-oxazine, etc.; and bisoxazine compounds suchas 2,2'-bis(5,6-dihydro-4H-1,3-oxazine),2,2'-methylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-ethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-propylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-butylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-hexamethylenebis(5,6-dihydro-4H-1,3-oxazine),2,2'-(1,4-phenylene)bis(5,6-dihydro-4H-1,3-oxazine), etc.

These compounds are added to the rubber composite excluding theadhesive-treated polyester cords in order to prevent amines in therubber from permeating the polyester, a reinforcing material, of therubber composite. The expression "to the rubber composite excluding theadhesive-treated polyester cords" referred to herein means "between theadhesive and rubber" and/or "in the rubber". This limitation is soimportant that the reason for it will be explained below. Thereinforcing cord for the rubber composite is adhesive-treated in orderto obtain a sufficient adhesion strength, and the temperature of thisadhesive-treating step needs to be 200° C. or higher. Consequently, whenthe foregoing compounds used in the present invention are added to thisstep or the preceding steps, the compounds are inactivated by thisheat-treatment to fail to obtain the effect of the present invention.The compounds, therefore, need to be added after this heat-treatingstep.

There is no particularly severe limitation to the amount of the compoundhaving a cyclic iminoether group. The effect can be noticed even with atrace amount, but generally, the compound is used in an amount of from0.01 to 20 wt.% based on the rubber composition.

The compound having a cyclic iminoether group of the present inventionreacts with the amine, and in carrying out this reaction, there may beused a catalyst for the ring-opening polymerization of a cycliciminoether compound as described, for example, in Polymer J., Vol. 3,No. 1, pp. 35-39 (1972) and "Polymerization Kinetics 7th series,Ring-opening Polymerization II", pp. 159-164, published byKagaku-Dojin-Sha Co. in 1973. Specific examples of such catalyst includefor example strong acids, sulfonic acid esters, sulfuric acid esters,organo-halogen compounds containing at least one halogen atom bonded tothe alkyl carbon in the molecule, Lewis acids, etc.

The strong acids include for example organic acids such asphenylphosphoric acid, methanesulfonic acid, benzenesulfonic acid,p-toluenesulfonic acid, dodecylbenzenesulfonic acid,naphthalene-α-sulfonic acid, naphthalene-β-sulfonic acid, sulfanilicacid, phenylsulfonic acid, etc., and mineral acids such as oxoacids(e.g. phosphoric acid, sulfuric acid, nitric acid) and hydroacids (e.g.hydrochloric acid, hydrobromic acid, hydroiodic acid, hydrogen sulfide).

The ulfonic acid esters include for example methyl p-toluenesulfonate,ethyl p-toluenesulfonate, n-butyl p-toluene-sulfonate, etc.

The sulfuric acid esters include for example dimethyl sulfate, diethylsulfate, etc.

Preferred examples of the organo-halogen compound are monohaloalkanesand polyhaloalkanes, and specifically, there are mentioned methyliodide, butyl chloride, butyl bromide, n-hexyl bromide, butyl iodide,lauryl bromide, n-octyl bromide, stearyl bromide, allyl bromide, ethanetetrabromide, etc.

Other preferred specific examples of the organo-halogen compound includefor example monohalomethylbenzenes (e.g. benzyl bromide,p,p'-dichloromethylbenzene), polyhalomethylbenzenes, α-bromo-n-propionicacid esters and α-bromoisobutyric acid esters.

Lewis acids include for example aluminum chloride, stannic chloride,vanadium chloride, vanadyl chloride, boron trifluoride etherate, etc.

The above catalysts may also be used in the rubber composite of thepresent invention, but the catalyst is not always limited to theforegoing specific examples, if it has the desired effect. It is amatter of course that the catalyst must properly be selected accordingto the composition of the rubber composite of the present invention.These catalysts may be used alone or in combination of two or more ofthem. The catalysts are used in an amount of from about 0 to about 5wt.%, preferably from 0 to 1 wt.% based on the weight of the oxazolinecompound.

Next, explanation will be given on why trapping the amine present in therubber composite of the present invention is effective to achievethermochemical stability of the rubber composite.

For example, the hydrolysis of polyethylene terephthalate (PET), arepresentative example of polyester fibers, is expressed by thefollowing equation: ##EQU1## wherein Ci represents an initial amount ofcarboxyl groups of the PET fibers (equivalent/10⁶ g), T represents ahydrolysis temperature (° K.) and t represents a hydrolysis time (hour).

Ammonolysis, which is a model reaction of the hydrolysis of PETcatalyzed by amines, is expressed by the following equation: ##EQU2##wherein Ci represents an initial amount of carboxyl groups of the PETfibers (equivalent/10⁶ g), T represents an ammonolysis temperature (°K.) and t represents an ammonolysis time (hour).

The comparison of the reaction rate constants of both reactions is shownin FIG. 1. The activation energy of the hydrolysis is 23.6 kcal/mole andthat of the ammonolysis is 12.5 kcal/mole. The practical temperature atwhich the rubber composite is used is 150° C. or less, so that it isobvious that the ammonlysis occurs markedly easier than the hydrolysisin this temperature region. Hereupon, the comparison of both reactionrates is shown in FIG. 2 with regard to a case where an initial amountof carboxyl groups at 100° C. is 10 equivalents/10⁶ g. Ammonolysis is areaction wherein ammonia neutralizes the terminal carboxyl group toproduce 1 molecule of water, and the water causes hydrolysis in thepresence of ammonia (base catalyst). From FIG. 2, it is easilyunderstandable that the rate of hydrolysis caused by the base catalystis incomparably faster than that of hydrolysis wherein the terminalcarboxyl groups act as an acid catalyst.

Consequently, it may be said that, in the region of practical use, theeffect of the terminal carboxyl group on the hydrolysis of the polyesterfibers is extremely little. On the other hand, when the amine permeatesthe polyester fibers, remarkable degradation of the fibers is caused.

The is the point of the present invention. That is, by reaction of theamine with the compound having a cyclic iminoether group added to therubber matrix, the bulkiness of the amine increases to make it difficultfor the amine to move within the rubber, and therefore permeation of thebulky amine into the polyester fibers naturally becomes extremelydifficult. As a result, it becomes possible to prevent the decompositionof both the polyester itself and polyester layer which participates inadhesion strength at the interface between the polyester surface andrubber layer, and thus, the retention of the tenacity and adhesionstrength of the polyester fibers markedly improves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrams illustrating the relationships between, on onehand, the rates of ammonolysis of PET fibers and hydrolysis of the samefibers in saturated steam, and on the other hand, the reciprocal of theabsolute temperature. It can be seen that the rate of hydrolysis isextremely slow as compared with that of ammonolysis at thelow-temperature side.

FIG. 2 shows a comparison of the dissociation degrees at 100° C. ofammonolysis of PET fibers and hydrolysis of the same fibers in saturatedsteam.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be illustrated with reference to thefollowing examples, but it is not limited to these examples.

EXAMPLE 1

Polyethylene terephthalate, its intrinsic viscosity being 1.0 asmeasured at 25° C. in a phenol/tetrachloroethane (6:4) mixed solvent,diethylene glycol content being 1.0 mole% and carboxyl group contentbeing 10 equivalents/10⁶ g, was melt-spun and stretched by the usualmethod to obtain polyethylene terephthalate yarns of 1500D (190filaments). The yarns obtained had a tensile strength of 13.5 kg and anelongation of 12.5%. Using the yarns, a two-ply cord of 38 t/10 cm intwist number for each of cable twist and ply twist was prepared andtreated with an RFL solution containing Vulcabond E [produced by VulnaxCo.; old name, Pexul (a trade name of ICI Co.)} which is a reactionproduct of resorcinol, p-chlorophenol and formaldehyde. The compositionof the treating solution was as follows.

    ______________________________________                                                       Part by weight                                                 ______________________________________                                        RF resin solution                                                             Water            332.4                                                        Caustic soda      1.3                                                         Resorcinol        16.6                                                        Formaldehyde (37%)                                                                              14.7                                                        subtotal         365.0                                                                     Pre-ageing: 25° C. × 6 hours                        RFL                                                                           RF resin solution                                                                              365.0                                                        VP latex         195.0                                                        SBR latex         50.0                                                        subtotal         610.0                                                        Vulcabond E + RFL                                                             RFL              610.0                                                        Vulcabond E      183.0                                                        total            793.0                                                                     Ageing: 24 hours                                                 ______________________________________                                    

The foregoing two-ply cords were dipped in this treating solution andtreated at a temperature of 240° C. for 2 minutes at a stretch ratio of3.0% to prepare adhesive-treated cords.

The blended rubber used for the test had the following composition:

    ______________________________________                                        Natural rubber (RSS #1)                                                                            100    parts by weight                                   Stearic acid         2                                                        Zinc white           4                                                        Sulfur               2.5                                                      SRF-carbon black     40                                                       Pine-tar             3                                                        N-phenyl-N-isopropyl-p-                                                                            0.75                                                     phenylenediamine                                                              2,2,4-Trimethyl-1,2-dihydro-                                                                       0.75                                                     quinone polymer                                                               Vulcanization accelerator MBT                                                                      0.8                                                      ______________________________________                                    

2,2'-(1,3-Phenylene)bis(2-oxazoline) (hereinafter referred to as1,3-PBO), a compound of the present invention, was added to the aboverubber in an amount of from 0 to 20 wt.%.

The foregoing adhesive-treated cords were completely embedded in thisrubber mixture and vulcanized in a mold at a temperature of 170° C. for3 hours under a pressure of 30 kg/cm² for the purposes of vulcanizationof the rubber and degradation of the composition at a high temperature.Thereafter, the treated cords were taken out of the vulcanized rubbercomposite and measured the for the residual strength and H adhesionstrength.

The thermochemical stability was expressed by strength retention andadhesion strength retention, the former being the ratio in percentage ofthe strength of the treated cords after vulcanization to that of thetreated cords before vulcanization, and the latter being the ratio inpercentage to H adhesion strength obtained by vulcanization at 170° C.for 30 minutes. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                      Amount of        Adhesion                                                     1,3-    Strength strength                                                     PBO added                                                                             retention                                                                              retention                                                    (wt. %) (%)      (%)                                            ______________________________________                                        A   (comparative example)                                                                         0         31.6   38.0                                     B   (present invention)                                                                           0.5       57.7   39.0                                     C   (present invention)                                                                           1.0       72.4   41.9                                     D   (present invention)                                                                           2.0       94.0   47.5                                     E   (present invention)                                                                           3.0       95.3   65.0                                     F   (present invention)                                                                           5.0       99.1   83.1                                     G   (present invention)                                                                           10.0      100.5  103.4                                    H   (present invention)                                                                           15.0      99.5   --                                       I   (present invention)                                                                           20.0      98.3   --                                       ______________________________________                                    

Any of the rubber composites B to I of the present invention exhibits aremarkable thermochemical stability as compared with the rubbercomposite A used as a control. It is noticed that an improvement in thethermochemical stability by the addition of 2 wt.% or more of 1,3-PBO isso great that a reduction in the strength cannot be seen.

EXAMPLE 2

The effect of the various additives of the present invention wasexamined using the same adhesive-treated cords (dip cords) and rubbercomposition as used in Example 1. The action of methylp-toluenesulfonate as a catalyst was also examined. The catalyst wasadded at the time of milling of the rubber. The strength retention and Hadhesion strength retention of the cords after 3 hours' vulcanization at170° C. are shown in Table 2. This table shows that the effect of theadditives of the present invention is remarkable.

                                      TABLE 2                                     __________________________________________________________________________                             Amount                                                                        added                                                                              catalyst                                                                           Retention (%)                                            Cyclic iminoether                                                                        (wt. %)                                                                            (wt. %)*                                                                           Strength                                                                           Adhesion                              __________________________________________________________________________    A (comparative example)                                                                     None       0    0    31.6 38.0                                  F (present invention)                                                                       1,3-PBO    3    0    95.3 65.0                                  J (present invention)    3      0.5                                                                              98.1 68.7                                  K (present invention)    3    1    99.1 70.2                                  L (present invention)    3    2    99.6 68.5                                  M (present invention)                                                                       2-Phenyl-2-oxazoline                                                                     5    0    92.3 60.1                                  N (present invention)                                                                       2,2'-Bis(2-oxazoline)                                                                    5    0    94.8 63.5                                  O (present invention)                                                                       2,2'-(1,3-Phenylene)bis                                                                  2    0    60.2 57.4                                  P (present invention)                                                                       (5,6-dihydro-4H-1,3-                                                                     2    1    98.8 72.7                                  Q (present invention)                                                                       oxazine)   4    0    97.4 81.6                                  __________________________________________________________________________

EXAMPLE 3

Polyarylate synthesized by the copolymerization of 40 moles ofp-acetoxybenzoic acid, 15 moles of terephthalic acid, 5 moles ofisophthalic acid and 20 moles of 4,4'-diacetoxydiphenyl was melt-spunand wound up at 680 m/min. The spun yarns obtained were heat-treated ata temperature of 320° C. for 3 hours in a nitrogen gas stream to obtain1005 denier fibers of 28.3 g/d in tenacity, 925 g/d in initial modulusand 3.1% in elongation. Using the fibers, a two-ply cord of 40 t/10 cmin twist number for each of cable twist and ply twist was prepared. Thedip-treatment was applied to the cords in order to give a property toadhere to the rubber. For the first treating bath there was used anaqueous dispersion of an epoxy resin, and for the second treating baththere was used the RFL solution. The treated cords thus obtained had thefollowing properties: tensile strength 30.5 kg; 6.8 kg elongation, 1.3%;and elongation at breakage, 3.0%. The treated cords were embedded inrubbers which are different in the amount of 1,3-PBO added, andvulcanized at a temperature of 170° C. The results are shown in Table 3.As is apparent from these results, the chemical stability ofpolyarylates, which have so far been said to be chemically unstable toamines in rubber, is remarkably improved by incorporating 1,3-PBO in therubber composite. Thus, there is obtained a prospect that polyarylatefibers can be put to practical use as a reinforcing material for heavyduty tires (for example tires for trucks and buses), which can beexpected from their properties.

                  TABLE 3                                                         ______________________________________                                        Content of 1,3-      Vulcanization time                                       PBO (wt. %)          15 min. 1 hour  3 hours                                  ______________________________________                                        H adhes-            comparative  9.8    3.7   2.6                             ion test                                                                             0                                                                      (kg/cm)            example                                                                        present      9.7   10.1   9.2                                    5                                                                                         invention                                                  Strength            comparative  96.2  70.3  17.7                             retention                                                                            0                                                                      (%)                example                                                                        present      102.4 101.2 98.8                                    5                                                                                         invention                                                  ______________________________________                                    

EXAMPLE 4

Poly(ethylenenaphthalene-2,6-dicarboxylate) having an intrinsicviscosity of 0.75 dl/g was melt-spun and stretched to obtain 1000-denierfibers having a tenacity of 8 g/d and an elongation of 5.6% at breakage.Using the resulting fibers, a two-ply cord of 40 t/10 cm in twist numberfor each of cable twist and ply twist was prepared, and to the cordswere applied the same dip-treatment and vulcanization-treatment as inExample 1. It was observed that the composite containing 5 wt.% of1,3-PBO was greatly improved in both the strength retention and adhesionstrength retention.

                  TABLE 4                                                         ______________________________________                                                  Content of 1,3- Retention                                                     PBO (wt. %)     (%)                                                 ______________________________________                                        H adhesion               comparative  41.7                                    test (%)    0                                                                                         example                                                                        present      85.3                                                5                                                                                         invention                                             Strength (%)             comparative  60.2                                                0                                                                                         example                                                                        present      99.5                                                5                                                                                         invention                                             ______________________________________                                    

EXAMPLE 5

The adhesive-treated cords used in Example 1 were dipped in awater/ethanol (1:2) mixed solution containing 20% of dissolved 1,3-PBO,air-dried and then further dried at a temperature of 80° C. on a vacuumdrier. The cords thus treated and the cords before the treatment wereeach embedded in the same rubber composition as used in Example 1 andvulcanized at a temperature of 170° C. for varying times of 30 minutesand 3 hours. The retentions of strength and adhesion strength after 3hours' vulcanization are remarkably improved as shown in Table 5. Thisresult shows that the cyclic iminoether of the present invention iseffective even when applied to either the surface or the vicinity of theadhesive-treated cords.

                  TABLE 5                                                         ______________________________________                                                   Dipping in 1,3-PBO                                                                          Retention                                                       solution      (%)                                                  ______________________________________                                        H adhesion   Not dipped      38.0                                             test (%)     (comparative example)                                                         Dipped          67.1                                                          (present invention)                                              Strength (%) Not dipped      31.6                                                          (comparative example)                                                         Dipped          98.5                                                          (present invention)                                              ______________________________________                                    

According to the method of the present invention, by incorporating acompound containing at least one cyclic iminoether group in the moleculein a rubber matrix excluding the portion of the adhesive-treatedpolyester fibers, there can be obtained a rubber composite which hasbeen greatly improved in the thermochemical stability of the polyesterfibers which are a reinforcing material, and besides which is free fromproblems such as breaking-out of scorch, etc.

The rubber composite obtained by the present invention canadvantageously be used in various processed rubber products, etc. bymaking use of its characteristics.

What is claimed is:
 1. A method of preventing degradation byamine-catalyzed hydrolysis of adhesive-treated polyester fiber cords ina rubber composite containing said cords as a reinforcing material andan amine, which comprises incorporating in said rubber compositeexcluding said adhesive-treated polyester fiber cords, anantidegradation effective amount, within the range of 0.01 to 20% byweight based on the weight of the rubber composite, of a compoundcontaining in its molecule at least one cyclic iminoether grouprepresented by the formula (I), ##STR3## wherein X represents anethylene group, substituted ethylene group, trimethylene group orsubstituted trimethylene group which makes the cyclic structure of theformula (I) a five-membered or six-membered ring.